Synthesis of r-glucosides, sugar alcohols, reduced sugar alcohols, and furan derivatives of reduced sugar alcohols

ABSTRACT

Disclosed herein are methods for synthesizing 1,2,5,6-hexanetetrol (HTO), 1,6 hexanediol (HDO) and other reduced polyols from C5 and C6 sugar alcohols or R glycosides. The methods include contacting the sugar alcohol or R-glycoside with a copper catalyst, most desirably a Raney copper catalyst with hydrogen for a time, temperature and pressure sufficient to form reduced polyols having 2 to 3 fewer hydoxy groups than the starting material. When the starting compound is a C6 sugar alcohol such as sorbitol or R-glycoside of a C6 sugar such as methyl glucoside, the predominant product is HTO. The same catalyst can be used to further reduce the HTO to HDO.

TECHNICAL HELD

The present invention relates to the synthesis 1,2,5,6-hexanetetrol(HTO), 1,4,5 hexanetriol, and 1,2,6 hexanetriol from C6 sugar alcoholsor R-glycosides.

BACKGROUND OF THE INVENTION

R-glycosides are known to be important intermediates for the productionof line chemicals, including sugar-based surfactants. Ordinarily,R-glycosides are prepared by Fischer glycosidation of an R-alcohol witha sugar, which involves the acid catalyzed formation of a glycoside bondbetween the acetal or ketal carbon of the sugar and the hydroxyl groupof the alcohol. The most common sugar is glucose. R-glycosides can alsobe prepared by acid catalyzed Fischer glycosidation of glucose residuesin a polysaccharide such as starch or cellulose with an alcohol, whichresults in cleavage of the glycosidic bonds in the polysaccharide viasubstitution of the alcohol moieties forming the tree glucosides. Strongacids, elevated temperatures, and elevated pressures are typicallyneeded. A mechanism compatible with milder conditions and utilizing aless expensive starting material, especially a starting material withotherwise limited applications, would be economically advantageous,especially on an industrial scale.

Cellulose is a primary component of plant matter, is non-nutritive, and.is not widely utilized outside of the paper and textile industries.Cellulose can be converted to glucose through acid or enzymatichydrolysis, however, hydrolysis is difficult due to the robustcrystalline structure of cellulose. Known acid hydrolysis methodstypically require concentrated sulfuric acid to achieve good yields ofglucose. Unfortunately glucose in the presence of concentrated sulfuricacid can degrade to form hydroxymethylfurfural (“HMF”) which in turn canfurther polymerize into a tarry substance known as humins. The formationof HMF and tarry humins negatively impacts the yield of glucose andrequires additional separation steps. Enzymatic hydrolysis methods knownin the art are also impractical for industrial scale conversion ofcellulose to glucose due to low reaction rates and expense and enzymesdo no hydrolyze cellulose that has been chemically modified.

Recently, Deng et. al., reported the direct conversion of cellulose andmethanol into methyl glycosides in the presence of an acid catalyst Denget al., Acid-catalysed Direct Transformation of Cellulose into MethylGlucosides in Methanol at Moderate Temperatures, 46 Chem. Comm. 2668-70(2010). Various dilute mineral and organic acids were tested, withsulfuric acid providing the best yield of methyl glycosides at 48%.Keggin-type heteropolyacids were also tested, with H₃PW₁₂O₄₀ yielding53% methyl glycosides. However, the conversion of cellulose in ethanolin the presence of H₃PW₁₂O₄₀ resulted in a decreased yield of 42% ethylglycosides. Solid acids were tested, with various forms of carbonbearing SO₃H groups giving the best yield of methyl glucosides at 61%.

More recently, Dora et al. reported the catalytic conversion ofcellulose into methyl glucosides over sulfonated carbon based catalysts.Dora et. al., Effective Catalytic Conversion of Cellulose into HighYields of Methyl Glycosides over Sulfonated Carbon Based Catalyst, 120Bioresource Technology 318-21 (2012). Carbon based catalysis containingSO₃H groups were synthesized and evaluated for the conversion ofcellulose in methanol. Specifically, macrocrystalline cellulose wasreacted with methanol and the sulfonated carbon, catalyst (50% by weightof the microcrystalline cellulose) at temperatures from 175° C. to 275°C. A maximum 92% yield of methyl glucosides was obtained at a reactiontime of 15 minutes at 275° C.

Turning to sugar alcohols, here are currently no known processes forproducing sugar alcohols (i.e. hexitols or pentitols such as sorbitoland xylitol) from alkyl glycosides by hydrogenation. Typically sugaralcohols are produced by heating unmodified sugars at elevated pressurein the presence of a hydrogenation catalyst.

Recently, Fukuoka. et al reported that sugar alcohols could be preparedfrom cellulose using supported platinum or ruthenium catalysts, whichshowed high activity for the conversion of cellulose into sugar alcoholswith the choice of support material being important. Fukuoka et al.,Catalytic Conversion of Cellulose into Sugar Alcohols, 118 Agnew. Chem.5285-87 (2006). The mechanism, involves the hydrolysis of cellulose toglucose followed by the reduction of glucose to sorbitol, and mannitol.However the yields were at best around 30% conversion to sugar alcohols,and the reactions took place at an elevated pressure of 5 MPa.

More recently, Verendel et al. reviewed one-pot conversions ofpolysaccharides into small organic molecules under a variety ofconditions. Verendel et al., Catalytic One-Pot Production of smallorganics from Polysaccharides, 11 Synthesis 1649-77 (2011).Hydrolysis-by-hydrogenation of cellulose under acidic conditions andelevated pressure was disclosed as yielding up to 90% sorbitol, althoughthese processes were categorized as “by no means simple.” The directhydrolysis-hydrogenation of starch, inulin, and polysaccharidehydrolysates to sugar alcohols by supported metals under hydrogenwithout the addition of soluble acids was also disclosed. Ruthenium orplatinum deposited on aluminas, a variety of metals supported onactivated carbon, and zeolites were reported as suitable catalysts forcellulose degradation. The effect of transition-metal nanoclusters onthe degradation of cellobiose was also disclosed, with acidic conditionsyielding sorbitol. A different study looked, at the conversion ofcellulose with varying crystallinity into polyols over supportedruthenium catalysts, with ruthenium supported on carbon nanotubes givingthe best yield of 73% hexitols.

There remains a need for cost-effective methods of producing sugaralcohols with high selectivity and through alternate pathways.

On yet another subject, the molecule 1,2,5,6-hexanetetrol (“HTO”) is auseful intermediate in the formation of higher value chemicals. HTO andother polyols having fewer oxygen atoms than carbon atoms may beconsidered a “reduced polyols.” Corma et al. discloses generally thathigher molecular weight polyols containing at least four carbon atomscan be used to manufacture polyesters, alkyd resins, and pofyurethanes,Corma et al., Chemical Routes for the Transformation of Biomass intoChemicals, 107 Chem. Rev. 2443 (2007).

Sorbitol hydrogenolysis is known to produce HTO, although typically thereaction conditions are harsh and non-economical. U.S. Pat. No.4,820,880 discloses the production of HTO involving heating a solutionof a hexitol in an organic solvent with hydrogen at an elevatedtemperature and pressure in the presence of a copper chromite catalyst.Exemplary starting hexitols include sorbitol and mannitol. Water wasfound to adversely affect the reaction speed requiring the reaction tobe performed in the absence of water and instead using ethylene glycolmonomethyl ether or ethylene glycol monoethyl ether as the sole solvent,which puts a solubility limit on the amount sorbitol that can bereacted. Under such conditions the maximum concentration of sorbitolthat was shown to be useful was 9.4% wt/wt in ethylene glycol monomethylether, which provided a molar yield of about 28% HTO. In a similarreaction where the sorbitol concentration was reduced to about 2% wt/wtin glycol, monomethyl ether, the molar yield of HTO was 38% however thelow concentration of reactants makes such a process uneconomical. Morerecently. U.S. Pat. No. 6,841,085 discloses methods for thehydrogenolysis of 6-carbon sugar alcohols, including sorbitol, involvingreacting the starting material with hydrogen at a temperature of atleast 120° C. in the presence of a rhenium-containing multi-metallicsolid catalyst. Nickel and ruthenium catalysts were disclosed astraditional catalysts for sorbitol hydrogenolysis, however thesecatalyst predominantly produced lower level polyols such as glycerol andpropylene glycol and were not shown to detectably produce HTO orhexanetriols.

There remains a need for improved cost-effective catalyst for producingHTO from sugar alcohols and a need for alternative substrates other thansugar alcohols.

On another background subject, the molecule2,5bis(hydroxymethyl)tetrahydrofuran (“2,5-HMTHF”) is typically preparedby the catalyzed reduction of HMF. This is impractical due to theexpense of HMF, harsh reaction conditions, and poor yields. For example,U.S. Pat. No. 4,820,880 discloses the conversion of HTO to 2,5-HMTHF inethylene glycol monomethyl ether with hydrogen at a pressure of at least50 atmospheres, in the presence of a copper chromite catalyst, at atemperature in the range of 180° C. to 230° C.

Overall, there is a need in the art to devise economical methods forconverting cellulose to alkyl glycosides, for converting alkylglycosides to sugar alcohols, for converting sugar alcohols to HTO andother reduced polyols, and for making useful derivatives of such reducedpolyols such as 2,5-HMTHF.

SUMMARY OF THE INVENTION

The present disclosure provides, in one aspect, methods of synthesizingR-glycosides from acetyl cellulose pulp substantially without, theformation of degradation products. These methods involve heating anacetyl cellulose pulp in the presence of an alcohol of the formula ROH,where R is a C₁-C₄ alkyl group, and an acid catalyst selected from thegroup consisting of phosphonic acid and a sulfonic acid, for a time andat a temperature sufficient to form an R-glycoside fraction from theacetyl cellulose pulp. In preferred practices the acetyl cellulose pulpis derived from a monocot species, for example, a species selected fromthe group consisting of grasses, corn stover, bamboo, wheat straw,barley straw, millet straw, sorghum straw, and rice straw. In exemplaryembodiments the acid catalyst is a sulfonic acid of the formula R¹SO₃Hwhere R is an alkyl or cycloalkyl group.

In another aspect the present disclosure provides methods ofsynthesizing sugar alcohols from alkyl glycosides. These methods includecontacting a solution containing an R-glycoside with a hydrogenationcatalyst for a time and at a temperature and a pressure sufficient toconvert the R-glycoside to a mixture comprising the sugar alcohol andROH, where R is a C₁-C₄ alkyl group. The hydrogenation catalyst maycontain copper and/or ruthenium. When the hydrogenation catalyst,comprises copper and the solution should contains less than 2 ppmsulfide anion and less than 1 ppm chloride anions. Exemplary rutheniumcatalysts are selected from the group consisting of ruthenium supportedon carbon, ruthenium supported on a zeolite, ruthenium supported onTiO₂, and ruthenium supported on Al₂O₃.

In another aspect the foregoing method are combined providing a methodof producing sugar alcohols from acetylated cellulose pulp that includesgenerating an R-glycoside from acetyl cellulose pulp as described above;and contacting the R-glycoside with a hydrogenation catalyst as furtherdescribed above.

In another aspect the present disclosure provides methods of making areduced sugar alcohol including at least one member selected from thegroup consisting of 1,4,5 hexanetriol, 2,6-hexanetetrol, and 1,2,5,6hexanetetro. These methods include contacting a solution comprisingwater and at least 20% wt/wt of a starting compound selected from thegroup consisting of a C6 sugar alcohol and a R-glycoside of a C6sugar,wherein R is a methyl or ethyl group, with hydrogen and a Raney coppercatalyst for a time and at a temperature and pressure sufficient toproduce a mixture containing one or more of the a reduced sugar alcoholswith a combined selectively yield of at least 50% mol/mol. In mostadvantageous embodiments of these methods the reaction solutioncomprises 20-30% wt/wt water and 45-55% of a C2-C3 glycol. In anexemplary embodiment the solution comprises 20-30% wt/wt water and50-55% wt/wt propylene glycol. These methods provide of a combinedselectivity yield for their reduced sugar alcohols of at least 70%mol/mol. One specific embodiment of these methods is a method of making1,2,5,6-hexanetetrol. This specific embodiment includes contacting asolution comprising 20-30% wt/wt water, 45-55% of propylene glycol andat least 20% wt/wt of a starting compound selected from the groupconsisting of C6 sugar alcohol and a R-glycoside of a C6 sugar, whereinR is a methyl or ethyl group, with hydrogen and a Raney copper catalystfor a time and at a temperature and pressure sufficient to produce amixture containing the 1,2,5,6-hexanetetrol with a selectively yield ofat least 35% wt/wt. In most advantageous embodiments the selectivityyield for 1,2,5,6-hexanetetrol is at least 40% wt/wt.

In yet another aspect, there is provided methods of makingtetrahydrofuran derivatives such as2,5-bis(hydroxymethyl)tetrahydrofuran from the reduced sugar alcohol. Inone embodiment these methods include contacting a mixture comprising1,2,5,6-hexanetetrol with an acid catalyst selected from the groupconsisting of sulfuric acid, phosphonic acid carbonic acid and a watertolerant non-Bronsted Lewis acid for a time and at a temperature and apressure sufficient to convert the 1,2,5,6-hexanetetrol to 2,5bis(hydroxymethyl)tetrahydrofuran. In exemplary embodiments thenon-Bronsted Lewis acid is a inflate compound such as of bismuthtriflate and scandium triflate. In other exemplary embodiments the acidacatalyst is sulfuric acid. In a preferred embodiment the acid catalystis phsosphonic acid.

In certain embodiments, the mixture further includes 1,4,5 hexanetrioland contacting with the acid catalyst further converts the 1,4,5hexanetriol to 2 hydroxyethyl tetrahydrofuran. In certain embodimentsthe method includes making 2 hydroxyethyl tetrahydrofuran by contactinga mixture comprising 1,4,5 hexanetriol with the same type of acidcatalysts. Further methods may further include separating the2-hydroxyethyl tetrahydrofuran from the2,5-bis(hydroxymethyl)tetrahydrofuran. In a particular furtherembodiment the separated 2,5 bis(hydroxymethyl) tetrahydrofuran iscontacted with a rhenium oxide catalyst for a time and a temperaturesufficient to convert the 2,5-bis(hydroxymethyl)tetrahydrofuran to 1,6hexanediol.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows synthesis of R glycosides from acetylated cellulose over anacid catalyst in the presence of an R alcohol and synthesis of sorbitolfrom R-glucosides via hydrogenolysis over a hydrogenation catalystaccording to certain aspects of the invention.

FIG. 2 shows synthesis of hexanetriols and 1,2,5,6 hexanetetrol viahydrogenolysis of sorbitol and/or a C6 R-glucoside over a Raney nickelcatalyst according to other aspects of the invention, and showssynthesis of 2,5 (hydroxymethyl) tetrahydrofuran from 1,2,5,6hexanetetrol, and synthesis 2-hydroxyethyl tetrahydrofuran from 1,4,5hexanetriol, each by contact with a non-Bronsted Lewis acid according toyet another aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Synthesis of R-glycosides from Acetyl Cellulose Pulp. The presentdisclosure provides, in one aspect, methods of synthesizing R-glycosidesfrom acetyl cellulose pulp in the presence of an alcohol and an acidcatalyst. “R” as used generically in chemical formulae throughout thepresent disclosure represents an alkyl moiety. Glycosides generallyrefer to a substance containing a glycosidic bond (i.e. a type ofcovalent bond that joins a sugar molecule to another functional group,in this case an alkyl moiety), while glucosides generally refer toglycosides derived from glucose.

The acetyl cellulose pulp most suitable for use in the methods of thepresent disclosure is derived from a monocot species. Preferably, themonocot species is selected from the group consisting of grasses, cornstover, bamboo, wheat straw, barley straw, millet straw, sorghum straw,and rice straw. More preferably the monocot species is corn stover. Theacetyl cellulose pulp may be prepared by any method known in theindustry. One non-limiting example of the preparation of an acetylatedcellulose pulp, disclosed in WIPO Publication No. WO 2013/044042,involves treatment of lignocellulosic biomass with a C₁-C₂ acid (i.e. anacid containing 1 or 2 carbon atoms) followed by washing with a C₁-C₂acid-miscible organic solvent.

The alcohols most suitable for use in the methods of the presentdisclosure are those containing between 1 and 4 carbon atoms: methanol,ethanol, propanol, butanol, and isomers thereof. The alcohol ispreferably present in at least a 5:1 weight ratio of alcohol to acetylcellulose pulp

The acid catalyst most suitable for use in the methods of the presentdisclosure sulfonic acids of the formula RSO₃H or phsosphonic acid.Suitable, but non-exclusive examples of sulfonic acids includedinonylnaphthalene sulfonic acid, 6-ammo-m-toluenesulfonic acid (alsoknown as 2amino-5-methylbenzene sulfonic acid), alkylbenzene sulfonicacids (sold as Calsoft® LAS-99, which is a linear alkylbenzene sulfonicacid comprising a minimum 97% of C10-C16 alkyl derivatives ofbenzenesulfonic acid), branched dodecylbenzene sulfonic acid (sold asCalimulse® EM-99), and alkylarylsulfonic acid (sold as Aristonic® acid).The acid catalyst may be homogeneous or heterogeneous. The acid catalystis preferably present in an amount of at least 0.5% by weight of thealcohol and for economic reasons, preferably not more than 4% by weightof the alcohol.

In a typical process the acetyl cellulose pulp is first washed in thealcohol of choice, which is most typically methanol or ethanol, althoughany C₁-C4 alcohol may be used. The washed acetyl cellulose pulp iscombined with the alcohol and an acid catalyst in a reaction vessel andheated for a time and at a temperature sufficient to form an R-glycosidefraction from the acetyl cellulose pulp. The reaction vessel is thencooled to room temperature. Typically the contents are filtered toremove residual unreacted pulp. The liquid fraction may be furthersubjected to standard separation methods such as liquid extraction ordistillation to yield a purified R-glycoside fraction.

In the methods for synthesizing R-glycosides provided herein, reactiontime and temperature can be varied. At temperatures above 250° C.degradation products negatively impact the yield of R-glycosides. Attemperatures below 150° C., the acetyl cellulose pulp is notsubstantially solubilized and the yield of R-glycosides is alsonegatively impacted. The preferred reaction temperature is therefore150-250° C. The range of reaction times in the methods provided hereinis typically between 15 minutes and 45 minutes. Heating the acetylcellulose pulp at these temperatures and times solubilizes the acetylcellulose pulp, solubilizes hydrophobic sulfonic acid catalysts, andallows for the formation of an R-glycoside fraction while avoiding theformation of significant amounts of degradation products such as HMF.

Typically, the yield of R-glycosides from these methods is between 20%and 60% of the weight of the starting sugars in the acetyl cellulosepulp. Other side products of the methods may include levoglucosan,levulinates, furfurals such as hydroxymethyl furfural (HMF), and somesoluble free sugars such as dextrose.

Synthesis of Sugar Alcohols from R-glycosides. The present disclosureprovides, in another aspect, methods of synthesizing sugar alcohols fromR-glucosides in the presence of hydrogen and a hydrogenation catalyst asdepicted in FIG. 1. An Sugar alcohols that can be synthesized by thepresent methods include, but are not limited to, sorbitol, mannitol,iditol, dulcitol, talitol, and 1,4-sorbitan.

The R-glycoside can be obtained from a commercial source or derived fromany known method in the industry. In certain embodiments the R-glycosideis derived from acetyl cellulose pulp according to the previouslydescribed methods, and therefore the alkyl moiety of the R-glycosidepreferably contains between 1 and 4 carbon atoms. Other catalysts suchas various copper catalysts may also be useful. When the hydrogenationcatalyst is selected as one containing copper, the R-glycoside shouldcontain minimal anions, specifically less than 2 ppm sulfide anions andless than 1 ppm chloride anions.

The hydrogenation catalyst is preferably acidic. Hydrogenation catalystscontaining ruthenium, including but not limited to ruthenium supportedon carbon, ruthenium supported on a zeolite, ruthenium supported onTiO₂, and ruthenium supported on Al₂O₃, particularly favor the synthesisof sugar alcohols. The hydrogenation catalyst is preferably present inan amount or 0.5-12.5% weight of the R-glycoside in exemplary practicesusing ruthenium on carbon the amount was about 5% by weight of theR-glycoside.

The methods include combining the R-glycoside, hydrogenation catalyst,and water in a reactor vessel. Air is removed from the reactor vesseland hydrogen is charged to a desired pressure at room temperature. Thereactor is then heated to a temperature for a time sufficient to convertthe R-glycoside to a mixture comprising a sugar alcohol. The temperatureshould be at least 150° C. and the pressure at least 600 psi. Lowertemperatures and pressures result in substantially reduced yield of thesugar alcohol. Suitable temperatures are between 160° C. and 220° C.Most typically the temperature should between between 170° C. and 190°C., with a temperature of about 180° C. being most preferred. Suitablepressures are 600-1000 psi, with exemplary pressures being about 850psi. The reaction time is typically 2-4 hours.

Under preferred conditions the R-glycoside conversion rate reachesnearly 100% with a molar conversion rate to sorbitol of at least 85% Incertain non-limiting examples using purified R-glycosides the molarconversion rate reached 97% or even 100%.

Synthesis of 1,2,5,6-hexanetetrol and hexanetriols. In another aspect,the present disclosure provides methods of synthesizing a desiredcompound including at least one member selected from the groupconsisting of 1,4,5 hexanetriol, 1,2,5,6 hexanetetrol, and1,2,6-hexanetriol, from a starting compound that is a C6 R-glycoside orC6 sugar alcohol present as at least 20% wt/wt in a solution comprisingwater by hydrogenation with hydrogen in the presence of a Raney coppercatalyst. The Raney copper catalyst may be obtained from a commercialsource (e.g., WR. Grace & Co, United States) or prepared by methodsknown to those of ordinary skill in the art. Typically the method ofpreparation of a Raney copper catalyst involves alkali treatment of acopper aluminum alloy to etch away aluminum front, a surface portion ofthe alloy.

Preferably, the Raney copper catalyst is deployed as a fixed bed in areactor and is present at 5%-30% of the weight of the starting compound.In contrast to the copper chromite catalyst described in U.S. Pat. No.4,820,080 or other copper catalysts such as sponge copper (see Example6) the reaction with Raney copper can be performed in the presence ofwater with high molar selectivity for 1,2,5,6 hexanetetrol, 1,4,5hexanetriol and 1,2,6-hexanetriol, which permits the starting materialto be dissolved to 50% wt/wt or more of the reaction mixture when wateris the only solvent, with the combined selectivity for the desiredcompounds is at least 50% mol/mol.

Although in some embodiments water may be the only solvent, inparticularly advantageous embodiments the solvent is a mixture of 20-30%wt/wt water and 45-55% wt/wt of a C2-C3 glycol. In this case thestarting material can be from 15% to 35% wt/wt of the reaction mixture.In the most advantageous embodiments the C2-C3 glycol is propyleneglycol. In preferred practices the starting material (C6 sugar alcoholor C6 alkyl glycoside) is at least 20% wt/wt of the reaction mixture. Inexemplary embodiments the starting material is about 25% wt/wt of thereaction mixture. While not being bound by theory, it is believed themixture of water and propylene glycol strikes an optimal balance ofhaving enough water to solubilize up to 35% of the starting materialwhile the presence of enough C2-C3 glycol permits more hydrogen to besolubilized in the reaction mixture and further prolonging the lifespanof the Raney copper catalyst. When the starting material is a C6R-glycoside or C6sugar alcohol the reaction with Raney copper underthese conditions has a high selectivity for HTO and 1,4,5 hexanetriolwith these combined species accounting for over 60% and in most caseover 70% of the molar yield. Typically the HTO itself accounts for atleast 35% and more typically at least 40% of the molar yield from thestarting material.

A first subset of the methods involves the synthesis of HTO fromC6R-glycosides in the presence of the Raney copper catalyst. TheR-glycoside can be obtained from a commercial source or derived from anyknown method in the industry. In certain embodiments the R-glycoside isan ethyl glucoside obtained from actylated cellulose pulp as previouslydescribed herein. The reaction, however, can use any R-glycoside wherethe R group is a C1 to C4 alkyl group. Most preferably the R group ismethyl or ethyl with the most commonly available glycosides being methylglucoside or ethyl glucoside.

A second subset of the methods involves the synthesis of HTO fromC6sugar alcohols in the presence of the same catalyst. The sugaralcohols can be obtained from a commercial source or derived from anyknown method in the industry. In certain embodiments the sugar alcoholsmay be obtained by hydrogenation of C6 sugars or C6R-glycosides. Forexample, sorbitol is typically obtained by hydrogenation of glucose overa Raney nickel catalyst. Ethyl glucoside may be obtained hydrogenationof an acetyl cellulose pulp according to the methods previouslydescribed herein.

The methods include in one aspect, combining the R-glycoside or sugaralcohol with water and optionally and more preferably with the C2-C6glycol in a reaction vessel preferably containing a fixed bed of Raneycopper. Air is removed from the reactor vessel and hydrogen is chargedto a specified pressure at room temperature. The reactor is then heatedto a temperature and for a time sufficient to convert the startingmaterials to-a mixture containing the desired materials, which in thecase of C6sugar alcohol or C6 R-glycoside will be a mixture of HTO and1,4,5 hexanetriol. Under the best reaction conditions over 98% of thestarting material is converted with a selectivity for HTO and 1,4,5hexanetriol being least 50% mol/mol when only water is used or greaterthan 60% and even greater than 70% when a combination of water and C2 orc3 glycol such as propylene glycol is used as the solvent. Under suchconditions HTO is least 35% and more preferably at least 40% of themo/mol yield from the starting material.

In the methods for synthesizing HTO provided herein, the pressure,temperature, and reaction time can be varied. Preferably the temperatureis between 175° C. and 250° C. In exemplary embodiments the temperature190° C.-215° C. The pressure is preferably between 500 psi and 2500 psi.In more typical embodiments the pressure is between 800 and 2000 psi. Incertain exemplary embodiments the pressure is about 1800 psi. In a batchreactor, the reaction time is preferably between 1 hour and 4 hours, andmore preferably is 3 hours. In a continuous reaction system the inputstream of starting materials and the flow rate of hydrogen are adjustedto obtain an optimal residence time of the starting materials in contactwith the Raney copper catalyst In typical laboratory scale examples, thehydrogen flow rate was 800-1000 milliliters/minute and the sorbitolsolution flow rate was 0.25 milliliters/minute obtaining an averageresidence time of 2 hours.

In addition to the major hexanetriols discussed above, the same methodsof hydrogenolysis of C6 sugars or R-glucosides produce other polyols,such as 1,2,5 hexanetriol, 1,2 butanediol 1,2,3 butanetriol, propyleneglycol, ethylene glycol and small amounts. Under conditions where HTOsynthesis is optimum, such as in the presence of propylene glycol andwater, 1,2 butanediol is the third major product made after HTO and1,4,5 hexanetriol.

Similarly, C5 sugar alcohols such as ribotol, xylitol and arabitol, andR-glycosides may also be subject to hydrogenolysis over Raney nickel asprovided herein, resulting in the production of 1,2,5 pentanetriol asthe dominant product, along with 1,2butanediol, 1,2,4 butanetriol,glycerol, ethylene glycol and propylene glycol. Erythritol may also bereduced by hydrogenolysis over Raney nickel to form 1,2 buatnediol asthe dominant product, along with 1,2,4 butatnetriol, 2,3 butatanediol,propylene glycol and ethylene glycol.

Intramolecular cyclization of polyols to tetrahydrofuran derivatives Animportant use of HTO and the hexanetriols, particularly 1,4,5hexanetriol, is that these molecules can readily undergo intermolecularcyclization in the presence of an acid to form useful tetrahydrofuran(THF) derivatives as shown in FIG. 2. The cyclization reaction is adehydration, which releases a water molecule form the polyols. The twodominant polyols from Raney nickel catalyzed hydrogenolysis of a C6sugar alcohol are HTO and 1,4,5 hexanetriol. HTO undergoes cyclizationto form 2,5-bis(hydroxymethyl)tetrahydrofuran (2,5 HMTHF) which isuseful starting material for the preparation of polymers or 1,6hexanediol. Under the same conditions 1,4,5 hexanetriol undergoescyclization to form 2-hydoxyethyl tetrahydyrofuran, which is a valuablesolvent and useful in the pharmaceutical field. Advantageously, the acidcatalyzed intramolecular cyclization of these compounds to theirrespective THF derivatives allows for easy separation of the THFderivatives from one another and from the starting sugar alcohols andhexane polyols that may remain unreacted.

As mentioned in preferred embodiments the acid catalyst is preferablyselected from the group consisting of sulfuric acid, phsosphonic acid,carbonic acid or a water tolerant non-Bronsted Lewis acid. It wassurprisingly discovered that phosphonic acid present as a homogenouscatalyst works exceptionally well, while phosphoric acid does not workat ail under most conditions. It may also be the case that heterogenousphosphonic acid catalysts such as were used for formation of glycosides,may also be useful.

A water tolerant non-Bronsted Lewis acid is a molecular species thataccepts electrons in the manner that hydrogen accept electrons in aBronsted acid, but uses an acceptor species other than hydrogen, andthat is resistant to hydrolysis in the presence of water. Exemplarywater tolerant non-Bronsted Lewis acids are triflate compoundexemplified herein by bismuth (III) triflate and scandium (III)triflate. Other suitable triflates include, but are not limited to,silver (I) triflate, zinc (II) triflate, gallium (III) triflate,neodymium (III) triflate, aluminum triflate, indium (III triflate, tin(II) triflate, lanthanum (III) triflate, iron (II) triflate, yttriumfill) triflate, thallium (I) triflate, gadolinium (III) triflate,holmium (III) triflate, praseodymium (III) triflate, copper (II)triflate, samarium (III) triflate, ytterbium (III) triflate hydrate, andnickel (II) triflate. Other suitable water tolerant non-Bronsted Lewisacids include, but are not limited to, bismuth (III) chloride, indiumchloride tetrahydrate, tin (II) chloride. aluminum chloride hexahydrate,silver (I) acetate, cadmium sulfate, lanthanum oxide, copper (I)chloride, copper (II) chloride, lithium bromide, and ruthenium (III)chloride. Preferably the acid catalyst is present in the range of 0.05%to 5% mol/mol of the starting materials in the reaction mixture. Stillanother alternative acid catalyst is carbonic acid, which can begenerated performing the reaction in water, under pressure and in thepresence of carbon dioxide.

The methods comprise combining HTO, any of the hexanetriols or a mixtureof the same with or without any residual unreacted sugar alcohol or 6CR-glycoside with the acid catalyst. In one practice the HTO and thehexanetriols may first be separated farm one another, for example bydistillation. In other practices the entire reaction mixture resultingfrom hydrogenolysis of the sugar alcohol or 6C R-glycoside over Raneycopper can be used and the subsequent THF derivative separatedthereafter by distillation. In the ease where the acid catalyst issulfuric acid or a non-Bronsted Lewis acid compound, the reactionmixture is preferably placed under vacuum of less than 0.4 psi andheated for a time sufficient to convert the hexanetriols and the HTO totheir respective tetrahydrofuran derivatives described above. When thereaction is done in the presence of carbonic acid, it performed underpressure, typically at least 625 psi.

In the methods provided herein, the temperature, pressure, and reactiontime can be varied. When the acid catalyst is not generated from CO₂,the temperature is preferably between 110° C. and 150° C. In methodsusing sulfuric acid or trilfate catalysts, the temperature, pressure,and reaction time can be varied. Preferably the temperature is between120° C. and 150° C. Temperatures below 120° C. fail to providesufficient thermal energy to effectuate ring closure. Temperatures above150° C. induce formation of unwanted side products. When a triflate,such as bismuth triflate or scandium triflate is used as the acidcatalyst, the temperature is more preferably about 130° C.

Further, the acid catalyzed cyclization preferably takes place undervacuum to facilitate removal of the water formed by the dehydration, andsubsequent recovery the desired THF derivative products. The vacuum ispreferably within the pressure range of 3.0 to 6.0 psi. Pressures below3.0 psi may cause some of the desired THF derivatives having low boilingpoints and high vapor pressures to evaporate. Pressures above 6.0 psifail to remove the water formed during the reaction. Lower pressuressuch as less than 0.4 psi, or even 0.1 psi are useful for the subsequentrecovery of THF derivatives with lower vapor pressures and/or higherboiling points.

Suitable reaction times are 1 to 4 hours. In some embodiments thereactions are complete in less 1-2 hours, and in some embodiments about1 hour.

The non-Bronsted Lewis acid catalysts useful herein are all watertolerant. Preferably the non-Bronsted Lewis acid catalyst is a metaltriflate. Preferably the non-Bronsted Lewis acid catalyst ishomogeneous. In particular embodiments, the non-Bronsted Lewis acidcatalyst is selected from the group consisting of bismuth triflate andscandium triflate. The inflate acid catalyst load is preferably between0.5 mole percent and 5 mole percent based on the starting polyol, andmore preferably present in an amount of 1 mole percent based on thestarting polyol materials.

In addition to the above compounds, other polyols obtained by Raneynickel catalyzed hydrogenation of C6 sugar alcohols or R-glucosidesinclude, 1,2,6 hexanetriol, 1,2,5 hexane triol and 1,2,4 butanetriol.Acid catalyzed cyclization of these compound predominantly forms1-methanol tetrahydropyranol, 5-methyltetrahydrofuran 2-methanol, and3-hydroxy tetrahydrofuran, respectively.

Further, a C5 sugar alcohols may also be reduced to lower polyols overRaney nickel. When a C5 sugar alcohol is used, the dominant reducedpolyol is 1,2,5 pentanetriol. Acid catalyzed cyclization of thiscompound predominantly forms tetrahydrofuran-2 methanol.

As shown in Table 1 below, clearly full conversion of the polyols totheir cyclized derivatives is possible. As demonstrated in Table 1 andby certain non-limiting examples, when nearly full conversion of thestarting sugar alcohol was achieved, up to a 83% mol/mol yield thecyclized THF derivatives can be obtained from their respective startingpolyol compounds. As used herein, “nearly full conversion” means atleast 97% of the starting compound or compounds are consumed in thereaction.

TABLE 1 % conversion to cyclic derivatives % cyclized products total %from total % cyclized converted conversion products products 1,2,5,6hexanetetrol, crude mixture 25% 17% 68.00% 1,2,5,6 hexanetetrol, crudemixture 28% 21% 75.00% 1,2,5,6 hexanetetrol, pure 99% 62% 62.63% 1,2,5pentanetriol, pure 64% 50% 78.13% 1,2,4 butanetriol, pure 88% 76% 86.36%1,2,5 hexanetriol pure 100%  83% 83.00%

The 2,5-bis(hydroxymethyl) tetrahydrofuran and other THF (and pyran)derivatives made from the polyols can be readily separated from oneanother and from unreacted polyols by distillation. The2,5-bis(hydroxymethyl) tetrahydrofuran can be subsequently converted to1,6 hexanediol via oxidation of the furan ring by contact with arhenium, oxide catalyst for a time and a temperature sufficient toconvert the 2,5-bis(hydroxymethyl)tetrahydrofuran to 1,6 hexanediol.Preferably the rhenium oxide catalyst further includes silicon oxide.

The examples that follow are provided to illustrate various aspects ofthe invention and are not intended to limit the invention in any way.One of ordinary skill in the art may use these examples as a guide topractice various aspects of the invention with different sources ofacetyl cellulose pulp, different alcohols, different acid catalysts,different hydrogenation catalysts, different polyol mixtures, ordifferent conditions without departing from the scope of the inventiondisclosed.

EXAMPLE 1 Preparation of Ethyl Glycosides from Aceytlated Corn StoverPulp

Acetylated corn stover pulp obtained by the method described in PCTPublication No. WO 2013/044042 was washed with ethanol, filtered, ovendried, and ground. A 75 milliliter autoclave reactor was charged with 2grams of the washed, ground pulp, 40 grams of denatured ethanol, and 0.2grams of methanesulfonic acid. The reactor system was heated to 185° C.After the set temperature was reached the reactor contents were held at185° C. for 30 minutes. The reactor was cooled to room temperature andthe contents were filtered. About 0.84 grams of dried, residual pulp wasremoved from 44.14 grams of filtrate. The yield of ethyl glucosides inthe filtrate as a weight percent of the sugars from the startingsolubilized pulp was 34%.

EXAMPLE 2 Preparation of Methyl Glycosides From Aceytlated Corn StoverPulp

Acetylated corn stover pulp was washed with ethanol, filtered, ovendried, and ground. A 75 milliliter autoclave reactor was charged with 2grams of the washed, ground pulp, 40 grams of methanol, and 0.2 grams ofmethanesulfonic acid. The reactor system was heated to 185° C. After theset temperature was reached, the reactor contents were held at 185° C.for 30 minutes. The reactor was cooled to room temperature and thecontents were filtered. About 0.93 grams of dried, residual pulp wasremoved from 44.72 grams of filtrate. The yield of monomethyl glucosidesin the filtrate as a molar percent of the starting sugars in the pulpwas 45%.

EXAMPLE 3 Preparation of Methyl Glycosides From Aceytlated Corn StoverPulp-Various Acids

The procedure described in Example 2 was followed using various reactiontimes and temperatures and various acids resulting in the molar yieldsof monomethyl glucosides shown in Table 2. EM-99 is a brancheddodecylbenzene sulfonic acid (sold as Calimulse®EM-99), LAS-99 isalkylbenzene sulfonic acids (sold as Calsoft® LAS-99), pTSA ispara-toluene sulfonic acid, MSA is methanesulfonic acid.

TABLE 2 Acid EM-99 LAS-99 pTSA MSA Temp C. 185 185 200 185 Time (min) 1515 30 30 molar yield of products from initial dextrose HMF 0.19 0.220.56 0.31 methyl 1.34 5.49 8.21 22.1 levulinate dextrose 3.47 2.98 4.32.39 levoglucosan 1.56 1.4 2.58 1.48 total 48.31 45.17 55.55 45.02monomethyl glucosides

EXAMPLE 4 Preparation of Sorbitol From Methyl Glucoside-LowerTemperature

A mixture of 80.1 grams of methyl glucoside, 10.1 grams of Ru/C, and 300milliliters of water was added to an autoclave reactor fitted withtemperature and pressure controllers. Air was removed by bubblinghydrogen through, the dip-tube 3 times. Hydrogen was charged at 850 psiat room temperature. The mixture was heated to 140° C. and held at thattemperature for 3 hours. The reactor was cooled to room temperature andthe remaining hydrogen was released. The reactor contents were filteredto remove the catalyst. The filtrate was evaporated under vacuum toobtain less than 5% yield of sorbitol and a large amount of unreachedmethyl glucoside.)

EXAMPLE 5 Preparation of Sorbitol From Methyl Glucoside-HigherTemperature

A mixture of 80.1 grams of methyl glucoside, 10.1 grams of Ru/C, and 300milliliters of water was added to an autoclave reactor fitted withtemperature and pressure controllers. Air was removed by bubblinghydrogen through the dip-tube 3 times. Hydrogen was charged at 850 psiat room temperature. The mixture was heated to 165° C. and held at thattemperature for 3 hours. The reactor was cooled to room temperature andthe remaining hydrogen was released. The reactor contents were filteredto remove the catalyst. The filtrate was evaporated under vacuum toobtain 97% yield of sorbitol and a small amount of unreacted methylglucoside.

EXAMPLE 6 Preparation of Sorbitol From Methyl Glucoside

A mixture of 80.1 grams of methyl glycoside, 10.1 grams of Ru/C, and 300milliliters of water was added to an autoclave reactor fitted, withtemperature and pressure controllers. Air was removed by bubblinghydrogen through the dip-tube 3 times. Hydrogen was charged at 850 psiat room temperature. The mixture was heated to 180° C. and held at thattemperature for 3 hours. The reactor was cooled to room temperature andthe remaining hydrogen was released. The reactor contents were filteredto remove the catalyst. The filtrate was evaporated under vacuum toobtain 100% yield of sorbitol.

EXAMPLE 7 Preparation of 1,2,5,6 Hexanetetrol From Methyl Glucoside inWater With Sponge Copper Catalyst—Comparative Example

A mixture of 80.1 grams of methyl glucoside, 24,8 grams of spongecopper, and 300 milliliters of water was added to an autoclave reactorfitted with temperature and pressure controllers. Air was removed bybubbling hydrogen through a dip-tube 3 times. Hydrogen was charged at850 psi at room temperature. The mixture was heated to 225° C. and heldat that temperature for 3 hours. The reactor was cooled to roomtemperature and the remaining hydrogen was released. The reactorcontents were filtered to remove the catalyst. The filtrate wasevaporated under vacuum to obtain 1,2,5,6-hexanetetrol (15% wt/wt) andsorbitol (85% wt/wt).

EXAMPLE 8 Preparation of 1,2,5,6 Hexanetetrol From Sorbitol in WaterWith Raney Copper Low Pressure

A Raney copper catalyst was loaded into a fixed bed reactor system. Thereactor was charged with hydrogen at 600 psi, and the hydrogen flow ratewas maintained at 1000 milliliters/minute. The reactor was heated to225° C. A solution of 50% wt/wt sorbitol and water was fed through thereactor system at a rate where LHSV=0.5 The conversion of sorbitol was98.5%, with a 5.8% weight yield of 1,2,5,6-hexanetetrol.

EXAMPLE 9 Preparation of 1,2,5,6 Hexanetetrol From Sorbitol in WaterWith Raney Copper—High Pressure

Raney copper catalyst was loaded into a fixed bed reactor system as inexample 7. Hydrogen was charged at 1800 psi, and the hydrogen flow ratewas maintained at 1000 milliliters/minute. The reactor was heated to205° C. Again a solution of 50% wt/wt sorbitol and water was led throughthe reactor system at a rate where LHSV=0.5. The conversion of sorbitolwas 73%, with a 28.8% selective weight yield of 1,2,5,6-hexanetetrol.Other polyols were present but not quantified.

EXAMPLE 10 Preparation of 1,2,5,6-Hexanetetrol From Sorbitol inWater/Propylene Glycol with Raney Copper

Solutions containing 25% wt/wt sorbitol, about 25% wt/wt water and about50% weight propylene glycol as shown in Table 3 were passed through aRaney copper fixed bed reactor system as described in Examples 8 and 9,at 210° C. and a. pressure of 1800 psi. The resulting reaction mixturewas analyzed for propylene glycol (PG), ethylene glycol (EG) 1,2hexanediol (1,2-HDO), 1,2 butanediol (1,2-BDO), 1,2,6 hexanetriol,(1,3,6-HTO), 1,4,5 hexanetriol (1,4,5-HTO) and 1,2,5,6 hexanetetrol(1,2,5,6-HTO) with the results shown in Table 4.

TABLE 3 Sam- Feed Jacket Pres- ple Propylene Sorbitol Water Temp sure H2flow ID Glycol % % % C. PSI LHSV ml/min XP1- 52.8 25.4 21.7 210 1800 0.4800 1116 XP1- 52.8 25.4 21.7 210 1800 0.4 800 1119 XP1- 50 25 25 2101800 0.4 800 1123 XP1- 50 25 25 210 1800 0.5 800 1124 XP1- 50 25 25 2101800 0.5 800 1125 XP1- 50 25 25 210 1800 0.5 800 1126 XP1- 50 25 25 2101800 0.5 800 1204

TABLE 4 Sorbitol Molar Selectivity (%) Sample Conver- PG 1,2- 1,2-1,2,6- 1,4,5- 1,2,5,6- ID sion % % EG HDO BDO HTO HTO HTO XP1- 99 52.513.23 3.14 15.76 5 32.71 35.08 1116 XP1- 99 52.39 12.43 3.33 15.58 5.3632.15 37.83 1119 XP1- 99 48.93 11.48 3.1 13.85 5.24 28.1 37.87 1123 XP1-99 50.2 12.2 3.28 14.84 5.3 25.72 35.56 1124 XP1- 99 50.32 14.03 3.8317.12 6.22 30.11 42.04 1125 XP1- 99 49.12 11.53 3.25 13.98 5.41 27.0338.38 1126 XP1- 99 49.04 11.58 3.23 13.94 5.61 26.83 38.49 1127 XP1- 9948.83 10.46 2.99 10.26 5.51 26.54 46.12 1204

EXAMPLE 11 Conversion of 1,2,5,6 Hexanetetrol2,5-bis(hydroxymethyl)tetrahydrofuran with Sulfuric Acid

A solution of 0.6 grains of concentrated sulfuric acid and 36 grains of1,2,5,6-hexanetetrol was reacted under vacuum (˜20 torr) at 120° C. for1 hour. The solution was cooled to room temperature and then neutralizedby adding 50 milliliters of water and 2 grams of calcium carbonate. Thesolution was filtered and then concentrated under vacuum to obtain abouta 96% yield of 2,5-bis(hydroxymethyl)tetrahydrofuran.

EXAMPLE 12 Conversion of 1,2,5,6 Hexanetetrol to2,5-bis(hydroxymethyl)tetrahydrofuran with Bismuth Triflate

A solution of 110 milligrams of bismuth triflate and 151.41 grains of asorbitol hydrogenolysis mixture containing 33% wt/wt1,2,5,6-hexanetetrol was reacted under vacuum (less than 5 torr) at 130°C. for 2 hours. The solution was cooled to room temperature. A sampleanalyzed by high performance liquid chromatography (HPLC) showed fullconversion of the 1,2,5,6-hexanetetrol and indicated that 93.4% of thetheoretical yield of 2,5-bis(hydroxymethyl)tetrahydrofuran was obtained.

EXAMPLE 13 Conversion of 1,2,5,6 Hexanetetrol to2,5bis(hydroxymethyl)tetrahydrofuran with Scandium Triflate

A solution of 89 milligrams of scandium triflate and 163.57 grams of asorbitol hydrogenolysis mixture containing 33% wt/wt1,2,5,6-hexanetetrol was reacted under vacuum (less than 5 torr) at 130°C. for 2 hours. The solution was cooled to room temperature. A sampleanalyzed by HPLC showed full conversion of the 1,2,5,6-hexanetetrol andindicated that 91.3% of the theoretical yield of2,5-bis(hydroxymethyl)tetrahydrofuran was obtained.

EXAMPLE 14

Conversion of 1,2,5,6 Hexanetetrol to2,5-bis(hydroxymethyl)tetrahydrofuran with Bismuth Triflate

A mixture of 544 milligrams of 1,2,5,6 hexanetetrol and 24 milligrams ofbismuth triflate was reacted under vacuum (200 torr) at 130° C. for 2hours. The resulting residue was cooled to room temperature. A sampleanalyzed by gas chromatography indicated that the residue contained1.24% (by weight) of the starting hexane-1,2,5,6-tetrol and 61.34% (byweight) of the desired (tetrahydrofuran-2,5,-diyl)dimethanol.

EXAMPLE 14 Conversion of 1,2,5,6 Hexanetetrol to2,5-bis(hydroxmethyl)tetehydrofuran with Phsosphonic Acid

A three neck, 500 mL round bottomed flask equipped with a PTFE coatedmagnetic stir bar was charged with 300 g of a mesophasic, off-white oilcomprised of ˜42 wt % 1,2,5,6-hexanetetrol and 3.44 g of phosphonic acid(H₃PO₃, 5 mol % relative to HTO). One neck was capped with a groundglass joint, the center with a sleeved thermowell adapter fitted with athermocouple, and the last a short path condenser affixed to a dry-icecooled 250 mL pear-shaped receiver. While vigorously stirring, themixture was heated to 150° C. under vacuum (20 torr) for 4 hours. Afterthis time, the vacuum was broken and residual, light colored oil cooled,and weighed, furnishing 3.06 g. GC analysis indicated that 95 mol % ofthe HTO had been converted and the selectivity yield for2,5-bis(hydroxymethyl)tetrahydrofuran was 88% mol/mol.

EXAMPLE 16 Preparation of Tetrahydrofuran-2-methanol from 1,2,5Pentanetriol

A mixture of 1.05 grams of pentane-1,2,5-triol and 57 milligrams ofbismuth triflate was reacted under vacuum (200 torr) at 130° C. for 2hours. The resulting residue was cooled to room temperature. A sampleanalyzed by gas chromatography indicated that the residue contained36.24% (by weight) of the starting pentane-1,2,5-triol and 50.37% (byweight) of the desired (tetrahydrofuran-2-yl)methanol.

EXAMPLE 17 Preparation of 3-tetrahydrofuranol from 1,2,4 Butanetriol

A mixture of 1.00 grams of 1,2,4 butanetriol and 62 milligrams ofbismuth triflate was reacted under vacuum (200 torr) at 130° C. for 2hours. The resulting residue was cooled to room temperature. A sampleanalyzed by gas chromatography indicated that the residue contained12.56% (by weight) of the starting butane-1,2,4-triol and 76.35% (byweight) of the desired tetrahydrofuran-3-ol.

EXAMPLE 18 Preparation of 5-methyltetrahydrofuran-2-methanol from1,2,5Hexanetriol

A mixture of 817 milligrams 1,2,5 hexanetriol and 40 milligrams ofbismuth triflate was reacted under vacuum (200 torr) at 130° C. for 2hours. The resulting residue was cooled to room temperature. A sampleanalyzed by gas chromatography indicated that the startinghexane-1,2,5-triol was completely converted and that the residuecontained 75.47% (by weight) of the desiredmethyltetrahydrofuran-2-methanol. Also produced at a 7.42% weight yieldwas the isomer 2-methyl-4-tetrahydropyranol.

EXAMPLE 19 General analytical protocol for ring cyclization

Upon completion of the reactant dehydrative cyclizations as described inexamples 11-18, a sample of the reaction mixture was withdrawn anddiluted with enough water to produce a 1-5 mg/mL solution. An aliquot ofthis was then subjected to high performance liquid chromatography (HPLC)for quantification using an Agilent 1200® series instrument andemploying the following protocol: A 10 μL sample was injected onto a 300mm×7.8 mm BioRad® organic acid column that was pre-equilibrated with an5 mM sulfuric acid mobile phase and flowed at a rate of 0.800 mL/min.The mobile phase was held isocratic and molecular targets eluting fromthe column at signature times determined by refractive index detection(RID). A quantitative method for each analyte was established prior toinjection, applying linear regression analysis with correlationcoefficients of at least 0.995.

1. A method of making 2,5-bis(hydroxymethyl)tetrahydrofuran, comprising:contacting a mixture comprising 1,2,5,6-hexanetetrol with an acidcatalyst selected from the group consisting of sulfuric acid, phosphonicacid, carbonic acid and a water tolerant non-Bronsted Lewis acid for atime and at a temperature and a pressure sufficient to convert the1,2,5,6-hexanetetrol to 2,5 bis(hydroxymethyl)tetrahydrofuran.
 2. Themethod of claim 1, wherein the non-Bronsted Lewis acid is a triflatecompound.
 3. The method of claim 2, wherein the triflate compound isselected from the group consisting of bismuth triflate, scandiumtriflate, and sulfuric acid.
 4. (canceled)
 5. (canceled)
 6. The methodof claim 1 wherein the wherein the mixture is contacted with thecatalyst under vacuum pressure of less than 0.4 psi.
 7. The method claim1 wherein the acid catalyst is sulfuric acid.
 8. The method of claim 1,wherein the acid catalyst is the non-Bronsted Lewis acid.
 9. The methodof claim 1, wherein the acid catalyst is carbonic acid formed by addingof CO₂ to the reaction mixture at a pressure sufficient to form carbonicacid.
 10. (canceled)
 11. (canceled)
 12. The method of claim 1 whereinthe mixture further includes 1,4,5 hexanetriol and contacting with theacid catalyst further converts the 1,4,5 hexanetriol to 2-hydroxyethyltetrahydrofuran.
 13. The method of claim 12 further including separatingthe 2-hydroxyethyl tetrahydrofuran from the2,5-bis(hydroxymethyl)tetrahydrofuran.
 14. The method of claim 1,wherein the acid catalyst is present in an amount between 0.5 mol % and5 mol % based on the amount of the 1,2,5,6-hexanetetrol.
 15. The methodof claim 1, further comprising separating the 2,5-bis(hydroxymethyl)tetrahydrofuran from the mixture and contacting the separated2,5-bis(hydroxymethyl)tetrahydrofuran with a rhenium oxide catalyst fora time and a temperature sufficient to convert the2,5-bis(hydroxymethyl)tetrahydrofuran to 1,6 hexanediol.
 16. The methodof claim 14 wherein the rhenium oxide catalyst further comprises siliconoxide.
 17. A method of making 2 hydroxy ethyl tetrahydrofurancomprising, contacting a mixture comprising 1,4,5 hexanetriol with anacid catalyst selected from the group consisting of sulfuric acid,phosphonic acid, carbonic acid, and a water tolerant non-Bronsted Lewisacid for a time, and at pressure and temperature sufficient to convertthe 1,4,5 hexanetriol to 2 hydroxy ethyl tetrahydrofuran.
 18. The methodof claim 17, wherein the water tolerant non-Bronsted Lewis acid catalystis a triflate compound.
 19. The method of claim 18 wherein the tiflatecompound is selected from the group consisting of bismuth triflate,scandium triflate, and sulfuric acid.
 20. (canceled)
 21. (canceled) 22.(canceled)
 23. The method claim 17 wherein the acid catalyst is sulfuricacid.
 24. The method of claim 17, wherein the acid catalyst is thewater-tolerant non-Bronsted Lewis acid.
 25. The method of claim 17,wherein the acid catalyst is phosphonic acid.